The Zenne Group () is a

group A group is a number of persons or things that are located, gathered, or classed together. Groups of people * Cultural group, a group whose members share the same cultural identity * Ethnic group, a group whose members share the same ethnic iden ...

rock strata In geology and related fields, a stratum (: strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as ...

in the

subsurface In geology, bedrock is solid rock that lies under loose material (regolith) within the crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface material. An exposed portion of bedro ...

of central and northwest

Belgium Belgium, officially the Kingdom of Belgium, is a country in Northwestern Europe. Situated in a coastal lowland region known as the Low Countries, it is bordered by the Netherlands to the north, Germany to the east, Luxembourg to the southeas ...

. The group consists of three formations, all from the

Ypresian In the geologic timescale the Ypresian is the oldest age (geology), age or lowest stage (stratigraphy), stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by th ...

and

Lutetian The Lutetian is, in the geologic timescale, a stage (stratigraphy), stage or age (geology), age in the Eocene. It spans the time between . The Lutetian is preceded by the Ypresian and is followed by the Bartonian. Together with the Bartonian it ...

ages (early

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

, 50 to 40 million years old). These formation have their shallow marine

facies In geology, a facies ( , ; same pronunciation and spelling in the plural) is a body of rock with distinctive characteristics. The characteristics can be any observable attribute of rocks (such as their overall appearance, composition, or con ...

in common. The three formations are: *the Aalter Formation, greenish

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is usually defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural ...

s and

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...

s, found in

East Flanders East Flanders ( ; ; ; ) is a Provinces of Belgium, province of Belgium. It borders (clockwise from the North) the Netherlands, Dutch province of Zeeland and the Belgian provinces of Antwerp (province), Antwerp, Flemish Brabant, Hainaut (provinc ...

and

West Flanders West Flanders is the westernmost province of the Flemish Region, in Belgium. It is the only coastal Belgian province, facing the North Sea to the northwest. It has land borders with the Dutch province of Zeeland to the northeast, the Flemis ...

. *the Brussels Formation,

marl Marl is an earthy material rich in carbonate minerals, Clay minerals, clays, and silt. When Lithification, hardened into rock, this becomes marlstone. It is formed in marine or freshwater environments, often through the activities of algae. M ...

s and sands, found in

Flemish Flemish may refer to: * Flemish, adjective for Flanders, Belgium * Flemish region, one of the three regions of Belgium *Flemish Community, one of the three constitutionally defined language communities of Belgium * Flemish dialects, a Dutch dialec ...

and

Walloon Brabant Walloon Brabant ( ; ; ) is a province located in Belgium's French-speaking region of Wallonia. It borders on (clockwise from the North) the province of Flemish Brabant (Flemish Region) and the provinces of Liège, Namur and Hainaut. Walloon Br ...

, Hainaut and

Namur Namur (; ; ) is a city and municipality in Wallonia, Belgium. It is the capital both of the province of Namur and of Wallonia, hosting the Parliament of Wallonia, the Government of Wallonia and its administration. Namur stands at the confl ...

. *the Lede Formation, calcareous sands, found in almost all central Belgium. Stratigraphically on top of the Zenne Group are the late Eocene sands and clays of the Maldegem Formation, which is not divided into a group. The Zenne Group is almost everywhere found on top of the early Eocene Ieper Group.

References

* (eds.); 2001: ''Paleogene and Neogene lithostratigraphic units (Belgium)'', Geologica Belgica 4(1-2), p. 135-152 Geologic groups of Europe Geologic formations of Belgium Lithostratigraphy of Belgium Eocene Series of Europe {{Europe-geologic-formation-stub